Intercom system

ABSTRACT

A digital wireless intercom system provides voice communications between selected mobile user stations via allocated radio channels. All communications flow via channels between the mobile stations and the base station. The base station includes a crosspoint processor for setting up desired communication links between users. A data store contains data identifying the preferences of each user, including the other users with whom communication links are to be set up. On receipt of a user ID from a mobile station, a correlator in the base station correlates the particular user with the channel being used by the mobile station of the user, so that the crosspoint processor can identify the channels in use for setting up the required communication links. The correlator dynamically updates the channel allocations as channels used by any particular user change. In this way, the crosspoint processor seamlessly follows channel changes, maintaining the required communication links with particular users. Separate wireless cells can be provided and the system supports roaming of individual mobile users from one cell to another whilst maintaining the required communication set-up by the crosspoint processor.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application ofInternational Application No. PCT/GB01/04033 filed Sep. 10, 2001 andpublished as WO 02/23932 on Mar. 21, 2002 in English.

FIELD OF THE INVENTION

This invention relates to intercom systems, for example such as are usedin the production of television programmes to enable a producer tocommunicate with various other people (for example camera man) involvedin producing the programme.

BACKGROUND TO THE INVENTION

Conventional intercom systems used in television studios comprise anumber of mobile units connected via cables to a remote base stationwhich coordinates audio signals to and from the mobile units. This sortof system can be inconvenient to use as a result of the constraintplaced by the cables on the movements of the users of the mobile units.

Such constraints are generally not present (or are less of a problem) ina wireless intercom system, but in this case, it is only possible forcommunications from a given unit to be either broadcast to all mobileunits simultaneously or to a selected one of the mobile units.

SUMMARY OF THE INVENTION

According to the invention, there is provided a digital wirelessintercom system comprising a base station and at least three mobileunits, transceiver means for sending digitally encoded wireless audiosignals to one or more of the mobile units, for reception thereby, inputmeans for receiving an audio input and converting it into such a signalprior to transmission of the signal by the transceiver means, eachmobile unit having output means connected to the transceiver means andoperable to convert a signal received thereby into an audio output, thebase station having selection means for selecting which mobile unit isto receive digitally encoded audio signals, wherein the selection meansis operable to select any number of mobile units to receive,substantially simultaneously, signals derived from the same audio input.

Thus, since each mobile unit receives digitally encoded audio signalsfrom the base station, the units to which the signals are to betransmitted can be readily controlled by the selection means so that agiven audio input can be broadcast to just one of the mobile units, toall the mobile units or to any number of mobile units between thoseextremes.

Thus, the invention provides an intercom system which has the advantagesof wireless signal links, whilst providing flexibility of selection ofmobile units to receive signals.

Preferably, the input means is provided on at least one of the mobileunits, and comprises a microphone and analogue to digital converterconnected to the transceiver means, the arrangement being such that themobile unit is operable to send digitally encoded audio signals to aselected other mobile unit or units via the base station.

Preferably, the input means is also provided at a plurality of othermobile units, and accordingly comprises a respective microphone andanalogue to digital converter at each of said other mobile units.

The mobile units are thus operable to establish signal links with othermobile units regardless of, and without affecting, the links alreadyestablished between other mobile units, as all of these links are madevia the base station. Thus, for example, if all the mobile units haveestablished communications links, over corresponding channels, with thebase station, each unit may communicate with any number of other unitswithout increasing the number of communications channels needed, so thatthe number of signal links may exceed the number of channels used by thesystem by a considerable margin.

Preferably, the output means is operable automatically to provide anaudio output at a given mobile unit in response to the selection of theunit by the selection means and the transmission of a digitally encodedaudio signal to the selected mobile unit. To that end, the transceivermeans may to advantage comprise a respective receiver at each mobileunit which receiver activates the output means at that mobile unit onreceipt of a signal, carrying selection data identifying that unit, fromthe base station.

Alternatively, the system may be arranged so that the receivers arepermanently active, but at any one time each receiver is operable toreceive signals from the base station only over a respective channel sothat said selection of mobile units is achieved by selecting whichchannels are to carry digitally encoded audio signals derived from agiven input.

The system may to advantage include means for transmitting text and/orpicture messages (composed at the base station or a mobile unit) to saidselected mobile unit or units, each of which units accordingly includesa visual display.

In this case, each mobile unit may to advantage be operable to display atext or picture message on receipt thereof by the base station, and thelatter may to advantage include a buffer memory for storing a textmessage for a selected mobile unit whilst another text message is beingtransmitted to or displayed-by the selected unit.

Preferably, the transceiver means, input means and output means aredevices which conform to the Digital Enhanced CordlessTelecommunications standard.

The selection means may be situated at the base station and controlledby a control unit, preferably forming part of a mobile unit, andoperable to transmit selection instructions to the selection means overthe wireless link provided by the transceiver means. At least one of themobile units may to advantage be operable only to transmit signals (forexample as a result of having no output means). Furthermore, at leastone mobile unit is preferably so arranged as to be able only to receivedigitally encoded audio and/or text signals.

As some mobile units may only be needed to receive or to transmitsignals, there would be no practical disadvantage in having two suchunits in a system, and these would give rise to the same bandwidthrequirements as a single “two-way” mobile unit.

The base station may to advantage include mixing means for mixing audiosignals received by two or more mobile units and transmitting thosesignals to a selected common mobile unit.

Preferably, the base station and mobile units have memories for storingdigital signals and are so configured that the mobile units transmitsignals to and receive signals from the base station only duringperiodic mobile unit and base station transmission intervalsrespectively, such that during a mobile unit transmission interval, onlyone mobile unit is operable to transmit signals to the base station,whilst during a base station transmission interval, only one mobile unitis operable to receive signals from the base station, the base stationbeing operable to transmit signals to the mobile units only duringperiodic base station transmission intervals.

Preferably, the mobile units further comprise digital data input andoutput ports for transmitting digital data to and receiving digital datafrom equipment connected to said ports, the mobile units and basestation being operable to transmit and receive signals carrying suchdata.

Preferably, the transceiver means comprises a respective radio frequencywireless transceiving forming part of the base station and each mobileunit.

Advantageously, the mobile units and base station are operable totransmit selection data and digital audio signals during first periodicmobile unit and base station transmission intervals, respectively, anddigital audio signals and text data signals during second periodicmobile unit and base station transmission intervals, respectively.Preferably, at least one of the mobile units does not include controlmeans for instructing the selection means on the base station, or thecontrol means may be de-activated by means of a signal from the basestation.

The invention also provides intercom apparatus comprising a basestation, said apparatus being capable of selectively establishing voicecommunication connections among a plurality of user stations and saidbase station being capable of communicating with each said user stationon a respective channel, said base station including:

-   -   (i) a data store containing        -   (a) respective user identification data identifying each of            a plurality of users of the apparatus, and        -   (b) respective personality data, for each said identified            user, including the user identification data of each other            user identified to have a voice connection with said            identified user;    -   (ii) a user and channel correlator receiving, from each said        user station, data correlating with the user identification data        of the respective user of the respective user station, and        correlating the user identification data of the respective user        with the respective channel of the user station of the        respective user; and    -   (iii) a cross point processor responsive to said user and        channel correlator to set up voice communication links amongst        said channels to provide voice connections between users in        accordance with said personality data.

With this arrangement, any user station can be given the “personalitydata” of any user of the intercom system, particularly the data definingthe required user connections. Once the user has identified him/herself(or rather his/her role or title), the apparatus correlates theparticular user with the channel being used by the user station of theuser, so that the user specific personality data can then be applied tothe channel. This has particular advantages for radio based intercomsystems as will be apparent from the following detailed description ofthe embodiments. The term “crosspoint processor” is used here toindicate any circuit or processing unit capable of setting up andchanging multiple connections between channels and is not limited todigital processing arrangements although digital processing is preferredas will be apparent in the following descriptions of examples of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of illustrative example,with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a digital wireless intercom systemembodying the invention, comprising a base station and three mobileunits;

FIG. 2 is a block diagram of a mobile unit of the system of FIG. 1;

FIG. 3 is a block diagram of the base station of the system of FIG. 1;

FIG. 4 is a block diagram of a digital wireless intercom systemillustrating different possible embodiments of the mobile units;

FIG. 5 is a simplified block diagram illustrating the essentialfunctionality of a digital intercom system embodying the invention;

FIG. 6 is a block diagram illustrating the base station of the system ofFIG. 5 in more detail;

FIG. 7 is a detailed block diagram of the base station control unit;

FIG. 8A is a block diagram of an active antenna;

FIG. 8B illustrates an E1 digital data frame;

FIG. 9A is a block diagram of an antenna splitter;

FIG. 9B illustrates a full E1 data frame as may be supplied to thesplitter of FIG. 9A;

FIG. 9C illustrates the E1 data frames for respective active antennaewhich are formed by splitting the frame of FIG. 9B; and

FIG. 10 is a block diagram of a mobile user station.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The digital wireless intercom system of FIG. 1 comprises base station 10and mobile units 12, 14 and 16. Base station 10 comprises a radiofrequency wireless transceiver 18 and a digital signal processor 20,transceiver 18 being operable to transmit signals to, and receivesignals from, the mobile units only during base station and mobile unittransmission intervals respectively. Signal processor 20 is operable tostore and process digitally encoded wireless audio signals and selectiondata.

Mobile unit 12 comprises a wireless transceiver 22, a selection datainterface 24, a digital signal processor 26, a loudspeaker 28 and amicrophone 30. Transceiver 22 is operable to transmit signals to, andreceive signals from, base station 10 only during mobile unit and basestation transmission intervals respectively. Interface 24 comprises akeypad (not shown) for entering selection data and a screen (not shown)for displaying selection data, the interface being operable to receiveselection data either transceiver 22 or the keypad. Signal processor 26is operable to digitise analogue audio signals from microphone 30, tostore the digital audio signals before transmission to base station 10and to reconstruct digital audio signals received from base station 10as analogue audio signals to be reproduced by loudspeaker 28.

Mobile units 14 and 16 respectively comprise wireless transceivers 32and 42, selection data interfaces 34 and 44, digital signal processors36 and 46, loudspeakers 38 and 48 and microphones 40 and 50.

In order to speak to another user of the intercom system, a user of, forexample, mobile unit 12 enters selection data using the keypad ofinterface 24, specifying, for example, mobile unit 14. The selectiondata is displayed on the screen of interface 24 and signal processor 26starts to digitise analogue audio signals from microphone 30. Theresulting digital audio signals are stored by signal processor 26 untila mobile unit transmission interval allocated to mobile unit 12, duringwhich transceiver 22 transmits the selection data and stored digitalaudio signals to base station 10.

The selection data and digital audio signals are received by transceiver18 and stored by signal processor 20, which has a digital audio signalmemory location and a selection data memory location allocated to eachmobile unit in the intercom system. The selection data memory locationallocated to each mobile unit stores a list of the mobile units thathave transmitted selection data specifying that mobile unit. Signalprocessor 20 sums the digital audio signals received from mobile unit 12with the digital audio signals (if any) already stored in the memorylocation allocated to mobile unit 14. Signal processor 20 generates dataindicating that mobile unit 14 has been specified in the selection dataof mobile unit 12. During a base station transmission interval allocatedto mobile unit 14 the summed digital audio signals stored in the memorylocation to mobile unit 14, and data indicating mobile unit 12 aretransmitted to mobile unit 14.

The summed digital audio signals and the data indicating mobile unit 12are received by transceiver 32 of mobile unit 14. The data indicatingmobile unit 12 is transmitted to interface 34 and displayed upon thescreen thereof to indicate to the user that mobile unit 14 is receivingsignals from mobile unit 12. The digital audio signals are transmittedto signal processor 36, at which they are reconstructed as analogueaudio signals and reproduced by loudspeaker 38.

If the user of mobile unit 14 wishes to speak to the user of mobile unit12, the process of establishing a signal channel between mobile units 14and 12 is as described above for mobile unit 12.

Alternatively, the user of, for example, mobile unit 12 may establish atwo-way signal channel with, for example, mobile unit 14 by enteringselection data specifying both mobile units 12 and 14. The selectiondata is displayed upon the screen of interface 24, transmitted to basestation 10 during a mobile unit transmission interval allocated tomobile unit 12 and stored by signal processor 18. The selection dataspecifying mobile unit 14 is stored in the selection data memorylocation allocated to mobile unit 12 and the selection data specifyingmobile unit 12 is stored in the selection data memory location allocatedto mobile unit 14. The selection data is transmitted to mobile unit 14by base station 10 during a base station transmission interval allocatedto mobile unit 14, at which the selection data is displayed on thescreen interface 34 to indicate to the user that mobile unit 14 isoperable both to transmit signals to, and receive signals from, mobileunit 12. The operation of mobile unit 14 is then the same as if the userthereof had entered selection data specifying mobile unit 12 using thekeypad of interface 34.

The mobile unit of FIG. 2 comprises a microphone 52, an analogue todigital converter (ADC) 54, an audio input buffer memory 56, a timedivision multiplexer (TDM) 58, an audio output buffer memory 60, adigital to analogue converter (DAC) 62, a loudspeaker 64, a transceiverbuffer memory 66, a Digital Enhanced Cordless Telephone (DECT) chipset67, a radio frequency wireless transceiver 68, a display screen 70, aselection data keypad 72, a digital data buffer memory 74 and a digitaldata input/output (I/O) port 76.

The base station of FIG. 3 comprises a wireless transceiver 78, a DECTchipset 80, a digital signal processor 82, a data buffer memory 84, aselection data memory 86 and a transmission memory 88.

In the following description the operation of the mobile units and basestation are described for the purpose of simplicity in terms of a singletransmission frequency. It will be appreciated that the DECT chipset infact uses ten frequencies simultaneously, such that in addition to thebase station the intercom system can comprise up to sixty mobile unitscapable of transmitting signals to and receiving signals from the basestation.

The operation of the mobile unit of FIG. 2 will now be described indetail. It is assumed that the user of the mobile unit has enteredselection data specifying at least one other mobile unit. Analogue audiosignals from microphone 52 are continuously digitised by ADC 54 and theresulting digitally encoded audio signals are stored by buffer memory56. Digitally encoded audio signals stored by buffer memory 60 arecontinuously reconstructed by DAC 62 as analogue audio signals, whichsignals are reproduced by loudspeaker 64. Assuming that an item ofdigital equipment is connected to I/O port 76, digital data signals areeither continuously transmitted from I/O port 76 to data buffer memory74 or continuously transmitted from data buffer memory 74 to I/O port76.

DECT chipset 67 constrains transceiver 68 to transmit signals to, orreceive signals from, the base station only during two mobile unittransmission intervals and two base station transmission intervals,respectively, allocated to the mobile unit. The two mobile unit and twobase station transmission intervals form part of a periodic transmissionframe of twelve mobile unit transmission intervals followed by twelvebase station transmission intervals. The two mobile unit and two basestation transmission intervals are separated by ten transmissionintervals, such that if, for example, the mobile unit is allocated theeleventh and twelfth mobile unit transmission intervals in eachtransmission frame, it will therefore also be allocated the eleventh andtwelfth base station transmission intervals.

The operation of the mobile unit during a single transmission frame willnow be described using the above example of a mobile unit that transmitssignals to the base station during the eleventh and twelfth mobile unittransmission intervals, and receives signals from the base stationduring the eleventh and twelfth base station transmission intervals.During the first five mobile unit transmission intervals of eachtransmission frame transceiver buffer memory 66 transmits digitallyencoded audio signals and any digital data signals and selection datareceived during the eleventh and twelfth base station transmissionintervals of the previous transmission frame to TDM 58. TDM 58 routesthe digitally encoded audio signals to audio output buffer memory 60,routes any digital data signals to data buffer memory 74 and any textand/or picture messages and/or selection data to display screen 70.

During the second five mobile unit transmission intervals of eachtransmission frame the digitally encoded audio signals stored in audioinput buffer memory 56 are transmitted to TDM 58 which transmits them totransceiver buffer memory 66. If any new selection data is entered uponselection data keypad 72 the selection data is transmitted to TDM 58 andthe selection data on display 70 is amended accordingly. Digital datafrom data I/O port 76 stored in data buffer memory 74 is transmitted toTDM 58. TDM 58 routes the digital data signals to transceiver buffermemory 66 once all the digitally encoded audio signals and any selectiondata have been transmitted. The signals and selection data are stored intransceiver buffer memory 66 as two data packets, the first comprisingcompressed digital audio signals and any selection data, and the secondcomprising compressed digital audio signals and the digital datasignals.

During the eleventh and twelfth mobile unit transmission intervalstransceiver 68 transmits the first and second data packets,respectively, to the base station.

The operation of the base station of FIG. 3 will now be described indetail. During the twelve mobile unit transmission intervals wirelesstransceiver 78 receives compressed digital audio signals and any digitaldata signals and/or selection data, which are transmitted to DECTchipset 80. DECT chipset 80 transmits the compressed digital audiosignals to signal processor 82. Any digital data signals are transmittedto data buffer memory 84 and any selection data to selection data memory86.

Selection data memory 86 contains a location corresponding to eachmobile unit in the intercom system. Each location stores a list of themobile units specified in the selection data of the mobile unitcorresponding to that location.

Transmission memory 88 and I/O port buffer memory 84 each contains alocation corresponding to each mobile unit. Each location intransmission memory 88 stores compressed digital audio signals, and eachlocation in I/O port buffer memory 84 stores digital data that are to betransmitted to the mobile unit corresponding to those locations.

When DECT chipset 80 has transmitted the compressed digital audiosignals from a particular mobile unit to signal processor 82, signalprocessor 82 addresses selection data memory 86 to examine the locationcorresponding to the particular mobile unit. For each mobile unit listedin the location in turn signal processor 82 addresses transmissionmemory 88 to examine the location corresponding to that mobile unit. Ifthe location already contains compressed digital audio signals signalprocessor 82 decompresses both the compressed digital audio signalsalready stored in the location and the compressed digital audio signalsreceived from DECT chipset 80. The decompressed signals are summed thencompressed and the compressed summed signals stored in the location. If,on the other hand, the location does not already contain compressedsignals the compressed digital audio signals received from DECT chipset80 are simply stored in the location.

For each mobile unit listed in the location in selection data memory 86signal processor 82 transmits the digital data signals (if any) to thelocation in I/O port buffer memory 84 corresponding to that mobile unit.

At the end of the twelfth mobile unit transmission interval signalprocessor 82 addresses selection data memory 86 to establish whether theselection data generated by the first mobile unit have changed since theprevious transmission frame. If the selection data have changed they aretransmitted to signal processor 82. Signal processor 82 addressestransmission memory 88, which transmits the compressed audio signalsfrom the location corresponding to the first mobile unit to the signalprocessor.

Signal processor 82 assembles the selection data (if any) and a portionof the compressed audio signals into a first data packet and transmitsthe first data packet to DECT chipset 80. DECT chipset 80 transmits thefirst data packet to transceiver 78 during the first base stationtransmission interval, which transmits the data packet to the firstmobile unit. In the meantime signal processor 82 addresses I/O portbuffer memory 84 to establish whether the location corresponding to thefirst mobile unit contains any digital data. If the location containsdigital data a block of the data is transmitted to signal processor 82,which assembles a second data packet comprising the remainder of thedigital audio signals from the location in transmission memory 88corresponding to the first mobile unit and the digital data (if any).

This process is repeated for the five other mobile units receivingsignals from the base station during the transmission frame.

The intercom system of FIG. 4 comprises a base station 90, a non-audiocontrol mobile unit 92, an audio receive mobile unit 94, an audiotransmit mobile unit 96, an audio transceiver mobile unit 98 and a datatransceiver mobile unit. FIG. 4 does not represent a practical intercomsystem but serves to illustrate the range of different types of mobileunit that may be used within an intercom system in accordance with theinvention.

The base station 90 is as described previously.

Non-audio control mobile unit 92 may take the form of a control panel atwhich the user may sit, or a belt pack that the user carries on hisperson. Non-audio control mobile unit 92 would be used to configure theintercom system by establishing the required signal channels between theother mobile units. In an intercom system comprising one or morenon-audio control mobile units the other mobile units would either nothave selection keypads fitted or their selection keypads would bedisabled.

Audio receive mobile unit 94 might be used in a television studio, forexample, by a cameraman who needs to receive instructions from thedirector during filming, but does not need to reply.

Audio transmit mobile unit 96 might be used by the presenter of atelevision programme to relay his voice to a sound recordist.

The audio transceiver is as described previously.

The data transceiver might be used to operate equipment such as camerasor lights by remote control, or to operate an autocue.

The use of the audio receive mobile unit in the intercom system meansthat an audio transmit mobile unit may also be used, transmitting duringthe two mobile unit transmission intervals that would otherwise beallocated to the audio receive mobile unit. Thus the intercom system mayhave more users than would be possible if all users used audiotransceiver mobile units but some users needed only either to transmitor receive.

FIG. 5 is a functional block diagram illustrating an embodiment of theinvention. A base station 101 provides voice communication links with anumber of user stations of which three are illustrated at 124, 126 and128. The communication links are provided over respective channels 118,119 and 120 via a transceiver unit 114 in the base station 101. Thechannels 118, 119 and 120 may be provided by cables, but in a preferredembodiment, the communication channels are radio channels. Thecommunication channels may provide digital links between the userstations and the base station 101 capable of carrying a duplex voicechannel for each user station, together with control data. In otherarrangements the voice channels may be analogue.

It may be noted that all voice communication links are between the basestation 101 and the respective user stations and there are no directcommunication links between user stations.

Within the base station 101, connections between user stations areprovided by a cross point processor 112 which enables voice data on anyone of the channels 118, 119 and 120 to be applied to a selected one orboth of the other channels. The various voice communication connectionsmade by the cross point processor 112 are controlled in accordance withdata contained in a user personality data store 116. The intercomapparatus described is intended particularly for use by a group ofusers, each of which may have predefined preferences. These preferenceswill include the identity of each other user with whom the user has tocommunicate, as well as other personal preferences such as volumesettings and other parameters. For example, the intercom may be used ina TV studio environment, whereupon the users may comprise the producerand various studio/production staff, such as cameramen, sound engineersetc. Each such user will have different standard requirements associatedwith their role. For example the producer may require to be heard overthe intercom by all other users, whereas, at the other end of the scale,junior production staff may require only to receive instructions. Thus,in general the users will have predefined requirements and settingsaccording to their role, and these requirements and settings arereferred to as the “personality data” of the user.

Referring again to FIG. 5, the store 116 contains the personality dataof the various users of the intercom apparatus within the appropriateenvironment. Accordingly, the personality data of each user is containedin the storage 116 in association with identification data for thatuser.

A feature of this embodiment of the invention is that any particularuser of the intercom apparatus need not be permanently associated with arespective communication channel between the base station 101 and theuser stations. When a particular user activates any one of the userstations 124 to 128, the user can first signal to the base station theidentification of the user, e.g. by an appropriate keypad selection atthe user station. This identification data is received by the basestation 101 over an appropriate one of the communication channels 118 to120 and is received in the base station 101 by a user/channel correlator122. A function of the user/channel correlator 122 is to correlate theidentification data of a particular user with the communication channelover which that data has been received, thereby enabling correlation ofthe particular user with one of the available communication channelsbetween the base station and user stations.

The personality data contained in the store 116 can then be associated,by the correlator 122, with the particular channel from the basesstation 101 on which the respective user's identification data has beenreceived. The cross point processor 112 is then set up to ensure thatthe channel now associated with the particular user is given the correctconnections to other channels associated with other users of theintercom system.

Importantly, this facility enables the cross point processor 112 to beset up dynamically, independently of which user operates which userstation. More importantly, if the communication links between the basestation 101 and user stations are by means of digital radio channels,the individual channels allocated to each user station can also bedynamically allocated, since the base station 101 functions to identifythe particular user on any dynamically allocated channel, and re-assignthe channel connections in the cross point accordingly.

FIG. 6 is a block diagram showing the base station 101 in slightly moredetail. The base station includes a control unit 102, essentiallyproviding the functionality described above, connected to an activeantenna 103. The active antenna 103 may provide a number of digitalcommunication channels with respective user stations, for exampleemploying the DECT standard. Thus the connection 104 between the controlunit 102 and the active antenna 103 may provide a number ofcommunication channels corresponding to the number of user stationswhich can be supported by the active antenna 103.

In order to increase the number of user stations supported by thecontrol unit 102, the unit 102 may be connected to an antenna splitter105 capable of sporting a number of separate active antennae 106. Then,if each active antenna can support m individual user stations, and theantenna splitter can support n active antennae, the connection 107between the control unit 102 and the antenna splitter 105 represents mncommunication channels. The control unit 102 of the base station 101 mayalso provide for additional trunk and control connections on lines 108,109 and 110. These connections may enable the base unit to be connectedwith other base units to form a network, with each base unit in thenetwork handling communication links with associated user stations.

FIG. 7 is a block schematic diagram illustrating a control unit 102 of abase station 101. The control unit incorporates an input data bus 632,an output data bus 634 and a control data bus 636. The buses 632, 634and 636 are Time Division Multiplex (TDM) buses having sufficientindividual time slots to accommodate the number of user stations on theintercom system.

The control unit comprises cross point processor 601, antenna interface602, and master processor 603, all of which are connected to the TDMbuses 632, 634 and 636.

The antenna interface 602 includes a compression codec 650 connected tothe input and output TDM buses 632 and 634, a microprocessor 646connected to the control bus 636 and associated with a message stack648. The codec 650 is in turn connected to an E1 interface 652 forinterfacing with an individual active antenna 103 or a number of activeantennas via an antenna splitter 105 (see FIG. 6). The E1 interface 652supports a standard 2.048 Mb/s E1 link providing a TDM digital link with32 time slots. As will be explained later, each antenna interface 602with a single E1 interface 652 can carry a maximum of 25 communicationchannels with respective user stations. The codec 650 encodes data forthese 25 channels from the output bus 634 and decodes data from thesechannels for application to the input bus 632. Importantly, each channelis associated with a particular time slot on the buses 632, 634 and 636.

Each of the channels communicating with a particular user stationincludes control data as well as voice data. The control data receivedfrom each user station on a respective channel is extracted by the codec650 and passed to microprocessor 646 for application as appropriate onthe control bus 636. The control or message data from a particular useris buffered by the microprocessor 646 in a message stack 648.

Crosspoint processor 601 comprises a multiply and accumulate (MAC) array638 connected to the input and output buses 632 and 634 via input andoutput buffers 644 and 640. A microprocessor 612 receives control dataon the control bus 636 and controls the MAC array 638 to provide therequired crosspoint functionality to establish the necessary voicecommunication links between the users of the system. The masterprocessor 603 comprises a clock generator 654 providing a system clock,a microprocessor 656 connected to the control bus 636, and a correlationmatrix store 660. The master processor 603 provides the functionality ofthe user personality data store 16 and user/channel correlator 22illustrated in FIG. 5. Thus, the microprocessor 656 provides thenecessary control information to the crosspoint processor 601 toestablish the required voice communication links. Each output applied bythe crosspoint processor to the output bus 634 can have a mix of anycombination of inputs from the input bus 632. The microprocessor 642instructs the MAC array 638 to load the appropriate digital samples fromthe input buffer 632 and multiply each by a unique coefficient derivedfrom the personality data in the correlation matrix 660. The results areaccumulated in the location in the output buffer 640 associated with therequired output slot.

The function of an active antenna which can be connected to the activeantenna interface 602 will now be described with reference to FIG. 8A.The active antenna includes an E1 antenna interface 702 to handle E1data frames in association with the antenna interface of the controlunit 102. A standard frame is illustrated in FIG. 8B. As known in theart, an E1 frame comprises 32 time slots S0 to S31. Slots S0 and S16 arereserved for synchronisation and link control signalling. Thus, 30×64Kb/s slots are available for communication use. The active antenna,however, only uses the first six slots of the E1 frame, of which one(the sixth) time slot is used for control signalling between the activeantenna and the control unit. This signalling between the active antennaand the control unit allows the active antenna to up date the basestation with the status of the user stations with which the activeantenna is in communication. For example, the active antenna wouldinform the control unit if a user station requests a change of channel,as will be explained later. Accordingly, an active antenna 700 cansupport five user stations, providing five channels (Ch1 to Ch5) on eachof slots S1 to S5 of the E1 data frame. Each individual channelallocated to a respective user station contains a mix of audio andcontrol data transmitted between the user station and the base station.

Referring to FIG. 8A, the E1 interface is connected to a message stack706, further connected with a digital base band codec 708. The codec 708provides interface with an rf module 710 for transmitting and receivingthe required radio signals to establish the channels to the five userstations. The codec 708 and E1 interface 702 are controlled by amicroprocessor 704. The message stack 706 provides buffering between thecodec 708 and the E1 interface 702.

FIGS. 9A, 9B and 9C illustrate an antenna splitter 800 which may beconnected to antenna interface 602 of the control unit, to provide morethan the basic five channels for communication with respective userstations. The antenna splitter 800 has a crosspoint switch 804 whichre-assigns time slots of a full E1 frame 826 (FIG. 9B) to provide fiveE1 frames as illustrated in FIG. 9C, each of which is then assigned to arespective antenna of the kind illustrated in FIG. 8A, via respective E1interfaces 806, 808, 810, 812, 814. In each case, a respective block ofsix time slots of the full frame 826 is re-assigned to occupy the firstsix time slots of the frame assigned to the respective antennae.

With this arrangement, all five blocks of time slots in a full E1 framegenerated by the codec 650 of an antenna interface 602 may be used forrespective user station channel data, so that a single antenna interface602 can establish communication with up to 25 user stations.

FIG. 10 illustrates a user station in the form a wireless mobile stationcapable of communicating with the active antenna described withreference to FIG. 8A. The user station may take the form of a mobilebelt pack to be worn by a user and includes an audio interface 500containing a microphone 501 and loudspeaker or earpiece 502 connected toan audio codec 503 via audio input and output amplifiers 504, 505. Thebelt pack may also comprise a processor section 506 providing userdisplays 507 and user buttons 508 associated with a microprocessor 509operating with a local settings store 510. The processor section 506operates to provide general control and housekeeping of the mobilestation as well as user interface functions via the user displays 507and user buttons 508. The microprocessor 509 generates a data streamwhich is communicated to the base station over the digital communicationlink established with the mobile station. A digital interface 511processes the digital audio and data signals received from andtransmitted to the base station via a radio interface 512. The radiointerface 512 incorporates a digital base band codec 513 and an rfmodule 514.

In the audio interface 500 conditioned audio signals (which may be fromone or more sources) are fed to the audio codec 503 which convertsanalogue signals into a linear digital format which are passed to thedigital interface 511. In the reverse direction, linear digital audiosignals received from the digital interface 511 are converted in theaudio codec 503 into analogue form for output via amplifier 505 and theearpiece or loudspeaker 502.

Digital interface 511 is responsible for processing of the digital audioand data signals that may be received from or transmitted to the basestation via the radio interface 512. The digital audio signal from theaudio interface 500 is compressed by codec 515 and the compressed audiois then multiplexed in the Mux/Demux unit 516 with the data stream fromthe microprocessor 509 in the processor section 506. This combinedsignal with a maximum data rate of 64 Kb/s is passed to the radiointerface 512 for transmission to the base station. Similarly, a 64 kb/sdata stream received from the base station is passed from the radiointerface 512 to be demultiplexed in the Mux/Demux unit 516 into itsdigital audio and data components. The data is passed to the processorsection 506, whereas the digital audio is decompressed to linear digitalform by codec 515 before supplying to the audio interface 500.

Importantly, the radio interface 512 in association with themicroprocessor 509 additionally performs the required quality of servicemanagement and link management operations to maintain the requiredcommunication link between the mobile station and the base station. Thismay be according to any appropriate standard low power digital radiocommunication protocol, such as the DECT protocol, or the Bluetoothprotocol. In either of these two examples, the radio interface 512continuously checks for a better radio channel amongst those availableto it. If a better channel is detected the mobile unit is arranged tosend a message to the active antenna at the base station to initiatenegotiations for a channel handover. This handover could involve movingto a different channel with the same antenna or to a channel on anotherantenna. Importantly, the base station is effective to track any channelhandover with a particular mobile station so that the crosspointprocessor is reprogrammed accordingly to maintain the desiredconnections and set up parameters for the user of the mobile stationwhich is transferring from one channel to another.

In operation, when a mobile station is first detected by the basestation, for example following power up, the mobile station and the, orone of the, active antennae are effective to allocate a channel forcommunication with the mobile station. In the example described, theallocated channel would be one of the five channels (Ch1 to Ch5) handledby a particular active antenna. If there are several active antennasavailable, the one selected by the system would be the one providing thebest channel performance at the mobile station.

It is an important feature of this embodiment of the invention, that anyparticular mobile station could be used by any user, that is to say auser having any particular set of preferences or “personality data” asdefined previously. The user uses the buttons 508 of the mobile stationto indicate the identity of the user. This identity information istransmitted by the mobile station to the base station, in which the useridentity is correlated with the specific system channel being used forcommunication with the mobile station of that user.

As explained previously, one antenna interface 602 (FIG. 7) can, in thisexample, maintain discrete communication channels with up to 25 mobileusers. Only 25 time slots of the E1 frame are used for audio. The 25different communication channels would correspond to five time slots ineach of five blocks of six time slots each in a full E1 data frame asillustrated in FIG. 9B. In addition, five further time slots of the dataframe, comprising the sixth time slot of each block of six slots, isused for synchronisation and control data. The codec 650 in the antennainterface 602 has, therefore, 30 individual compression codecs, one foreach of the 30 used time slots of the E1 data frame. The codec 650interfaces the E1 data frame with the TDM input and output data buses632 and 634 of the base station, so that each time slot of the E1 dataframe is permanently associated with a unique time slot on the TDM buses632 and 634. It should be understood that the buses 632 and 634 wouldnormally provide a larger number of time slots than the E1 data frame,and in this example, sufficient time slots may be available on thesystem buses of the base station to enable the base station toaccommodate 200 full duplex communication channels with respective userstations.

It should be appreciated, therefore, that the base station, asillustrated in FIG. 7, could incorporate a further antenna interfaceproviding communication with up to a further 25 individual userstations. The 30 time slots from the E1 frame associate with theadditional antenna interface would then be uniquely associated with afurther 30 time slots on the system data buses, different from the 30time slots associated with an antenna interface 602.

In general, it can be seen therefore, that each particular radio channelwhich can be used for communication with a user station will be uniquelyassociated with a particular time slot on the system bus. The masterprocessor of the base station operates, on receipt of a useridentification data from a user station communicating via an allocatedradio channel, to correlate the personality data for that user with thechannel allocated by the system to the user station of that user, andhence to a particular time slot of the main system buses. Similarly, themaster processor 603 correlates all the other users which have “loggedon” to the system with time slots on the main system buses correspondingto the allocated radio channel for the respective user. The cross pointprocessor 601 can then be controlled by the master processor 603 to setup appropriate cross point links between the correlated time slots ofthe main system bus, to provide the required communication links betweenthe users.

Referring again to FIG. 7, the base station control unit illustratedalso comprises a digital trunk interface 612, an analogue trunkinterface 600 and a bus extension interface 622, as well as an internetinterface 658 in the master processor 603. These interfaces may be usedfor connecting multiple base stations together to expand the intercomsystem geographically and/or in terms of the number of available mobilestations. Connections between base stations may be set up in threedifferent ways.

For base stations which are physically close to each other, they may beconnected together via bus extension interfaces 622 on each basestation. These essentially interconnect the input buses 632 and controlbuses 636 of the two base stations so that the two stations essentiallyoperate as one. The bus extension interface 622 comprises a datainterface 624 with a message stack 630 buffering control data from or tothe control bus 636. Audio data on the audio input bus 632 is sharedwith the audio input bus of the other base station via a TDM audiointerface 626 and a TDM frame store 628.

The second method of interconnecting two base stations is via theanalogue trunk interface 600. The interface 600 comprises an audiointerface 604 which receives audio data from the output bus 634 via anA-to-D and D-to A converter 608, and similarly feeds received analogueaudio to the input data bus 632 via the converter 608. Control databetween the control buses 636 controls operation of the converter 608via a microprocessor 610, which in turn supplies corresponding controldata to the other base station via a data interface 602.

Instead of providing the data interface 602 in the analogue trunkinterface 600, the data transfer can be performed by means of theethernet interface 658 directly between the microprocessors 656 of themaster processors 603 of the two base stations.

A third method of connection is via digital trunk interface 612 on eachbase station. This is arranged essentially to create an E1 typeinterface between the base stations, enabling 30 channels of data to becommunicated between the base stations. All 30 slots of the E1 frame canbe used for audio in the links between base stations. For this purpose,the digital trunk interface 612 comprises a compression codec 618 an E1interface 620, together with a microprocessor 616 buffered by a messagestack 614. When using a digital trunk, control data to be communicatedbetween base stations can either be multiplexed with the audio data andsent over the E1 link, so that only 25 slots may be available for audio,or it can be sent over the Ethernet link as for the analogue trunk,whereupon all 30 E1 slots can be used for audio. If more than 25 (or 30as the case may be) channels of data are to be connected between the twobase stations, additional codec and E1 interfaces may be employed.

When multiple base stations are connected together by any of the abovetechniques, the master processors 603 in each base station ensure thatthe correlation matrix store 660 contains correlation data for each ofthe users of the whole system. Thus any updates to the correlationmatrix store on one base station, e.g. caused by a mobile station beingreallocated to a different channel, is communicated to the other basestation or base stations to provide corresponding updating of therespective correlation matrix store in the master processor of eachother base station. In this way, each base station keeps track of thechannel, and hence main system bus time slot allocation of each user ofthe system, so that the cross point processors of each base stationseamlessly follow channel changes and maintain the desired communicationlinks between users.

The possibility was mentioned above of a user station initiating achannel change on detecting a better available channel in the digitalradio system. The better channel could be another channel from the sameactive antenna (five different channels being available in the exampledescribed). However, the requested new channel could be a channel ofanother active antenna from the same base station, or even activeantenna from a different base station. In any case, when a base stationreceives a request from a particular user station to be allocated to adifferent channel, the new channel is assigned to the user associatedwith the user station in addition to the existing channel assignment, sothat the cross point processor sets up the additional communicationlinks simultaneously for the old and new channels of the user stationrequesting transfer. If the new requested channel is accessed via adifferent base station, because the correlation matrix store data,including the new requested channel data, is shared between all basestations, the cross point processor of the new base station sets up theappropriate communication links for the new requested channel, so thatinput and output data from the user interface requesting change issimultaneously received on the new channel via the appropriate activeantenna and antenna interface of the second base unit.

After a short period, sufficient to ensure that the new channel has beenestablished, the system releases the original channel, so thatsubsequent communications with the user station continue only on the newchannel.

Importantly, this enables full roaming capability of mobile userstations without loss of the required preferences and voice connectionsdesired for the user of the mobile station.

For interconnections between base stations via trunk interfaces, thedigital trunk interface 612 may provide only a smaller number ofdiscrete digital channels for communication between base stations, thanthe total number of system users. Similarly, the number of audioanalogue channels provided by the analogue trunk interface may belimited. In this case, each available channel of the trunk interface isassigned to a unique time slot of the system buses in each base station.The master processor of each base station has, as explained above, a mapof the users which are intended to be in communication with each other,correlated with the allocated time slots for the user stations of thoseusers. In a particular base station, at least the radio channelsavailable via active antennae connected to that base station have a oneto one correspondence with system time slots of the buses 632, 634 and636 of the respective base station. The digital-trunk interface 612connecting the base station to a second base station, for example via anE1 interface, provides 30 time slots in the communication link betweenthe two base stations and these time slots should have a one to onecorrespondence with additional time slots in the system buses 632, 634and 636.

When the master processor 603 identifies a communication link to be setup with a radio channel associated with a different base station, thecross point processor 601 of the first base station is controlled toapply the required digital output signal to one of the time slots on theoutput bus 634 associated with the digital trunk interface. At the sametime, the master processor 603 signals the other base station, either bythe ethernet interface 658, or by means of control data on the controlbus 636 sent via the digital trunk interface 612, to indicate to theother base station the target radio channel for the data on theparticular E1 interface time slot of the digital trunk interface. Theother base station receiving the audio from the first base stationapplies it to its input bus in the time slot uniquely associated withthe E1 time slot of the digital trunk. The audio is then applied by thecrosspoint processor of the other base station to an appropriate outputbus time slot mixed as required with other audio sources from othermobile units currently handled by the other base station or receivedover other trunk lines from further base stations.

In the above description, the “personality data” of each user of theintercom system is described as predefined and stored in the correlationmatrix store 660 of the base station. However, in practice, thepersonality data, including data defining the desired user connections,may be altered by operation of user buttons 508 on the user station of aparticular user. For example, if the producer wishes to speak privatelywith a particular other member of the production staff, the producer mayselect an appropriate code for the other user on the user buttons of theproducer's mobile station or belt pack. The button selection istransmitted by the mobile station to its base station and the dataalters the set up in the correlation matrix store so that the crosspoint processor sets up the desired new connection.

It should also be understood that the personality data of each user mayinclude the degree of control which that user is entitled to. Forexample, only selected buttons on the belt pack of the user may beenabled. This user station set up data is retrieved from the correlationmatrix store of the base station and transmitted to the user station.Whereupon the user station microprocessor applies the required settingsenabling buttons, and providing displays, as appropriate. The user datais supplied from the base station in response to the user identificationdata transmitted by the user station at the start of a session.

1. Intercom apparatus comprising a base station, said apparatus beingcapable of selectively establishing voice communication connectionsamong a plurality of user stations and said base station being capableof communicating with each said user station on a respective channel,said base station including: (i) a data store containing (a) respectiveuser identification data identifying each of a plurality of users of theapparatus, and (b) respective personality data, for each identifieduser, including the user identification data of each other user intendedto have a voice connection with said identified user; (ii) a user andchannel correlator receiving, from each said user station, datacorrelating with the user identification data of the respective user ofthe respective user station, and correlating the user identificationdata of the respective user with the respective channel of the userstation of the respective user; and (iii) a crosspoint processorresponsive to said user and channel correlator to set up voicecommunication links amongst said channels to provide voice connectionsbetween users in accordance with said personality data.
 2. Apparatus asclaimed in claim 1, arranged for wireless communication with a pluralityof wireless mobile stations on respective channels among a plurality ofpossible wireless channel said base station further comprising a channelallocator controlling allocation of said respective channels. 3.Apparatus as claimed in claim 2, wherein said channel allocator isoperative, in response to detecting a mobile station, to allocate anunused channel for communication with said detected station, said userand channel correlator correlating said user identification datareceived from said detected station with said allocated channel. 4.Apparatus as claimed in claim 3 wherein said channel allocator isfurther operative, in response to a predetermined wireless transmissionparameter, to reallocate a different wireless channel to any of themobile stations, said user and channel correlator being responsive tosaid channel reallocation to correlate said user identification datafrom said one of the mobile stations with the unit allocated differentwireless channel.
 5. Apparatus as claimed in claim 3, wherein saidchannel allocator is responsive to a new channel request from a mobilestation.
 6. Apparatus as claimed in claim 1 wherein said base stationincludes an interface for communicating data with a further said basestation, said data including at least said user personality data. 7.Apparatus as claimed in claim 6, wherein said base station interface isarranged to provide voice communication links between base stations,whereby voice communication connections can be set up between userstations communicating with different base stations.
 8. Apparatus asclaimed in claim 1 comprising said base station in combination with atleast one user station.